There are applications in which it is desirable to operate a drum to raise or lower a load at the end of a cable wound on the drum and in a coordinated manner to operate a piston to drive a reversible mechanism such that the mechanism moves in one direction as the drum rotates to lower the load at the end of the cable and in the opposite direction as the drum is rotated in the opposite direction to raise the load.
In an earlier construction the electric motor was external to the drum and operated an external pump driving a hydraulic motor. Only the hydraulic motor was carried in the drum. The resulting hydraulic lines were of significant length and there was a complication in matching the pump output to the hydraulic motor. The result was that the installation was more complicated, the hydraulic line losses were substantial, space was not well utilized and the system was generally somewhat inefficient.